Carburetor



Jah.- 19, 1931. D, 'FIRTVH' 068,127

CARBURETOR Filed May 9, 1934 f 37 @eff/W."

Patented Jan. 19, 1937 getan? PATENT FEQE l CARBURETOR David Firth, Flint, Mich., assignor to Marvel Carbureter Company, Flint, Mich., a corporation of Illinois Application May 9, 1934, Serial No. '724,795

10 Claims.

The invention relates to a carburetor for an internal combustion engine and has as its general object to provide a carburetor of novel and improved construction resulting in efficient operation and high fuel economy at all engine speeds.

A more particular object of the invention is to provide a carburetor of novel and improved construction having a suction valve controlled highspeed jet continuously supplied with fuel through a calibrated jet and an auxiliary fuel supply for the high speed jet supplying additional fuel thereto during the power range of throttle openlng.

Another object of the invention is to provide an improved carburetor in which vapor lock is prevented.

A further object is to provide a novel and improved thermostatic means automatically varying the extent of throttle opening when the engine is idling to prevent stalling when the engine is cold.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a View partially in elevation and partially in section of a carburetor embodying the features of the invention.

Figure 2 is a fragmentary detail sectional view showing the valve controlling the auxiliary fuel supply.

Figure 2a is a fragmentary View taken along line Zal-2a of Fig. 2 showing the contour of the cam controlling the valve.

Figure 3 is a detailed View showing the construction of the thermostatic idling speed control. The view is taken in a plane tangent to the riser at the point of support of the control and looking toward the front in Fig. 1.

While the invention is susceptible of various modifications and alternative constructions, it is here shown and will be described hereinafter as embodied in a dual carburetor of the up-draft type. It is not intended, however, that the invention is thereby to be limited to use in an updraft carburetor but it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined by the appended claims.

The carburetor shown comprises a main body member 5, without top or bottom wall, and a fuel bowl 6 bolted to the main body member and having a wall portion l extending below and closing the bottom of the member. Within the body member 5 is a mixing chamber 8 receiving air through an inlet opening 9 in communication with an air intake tube I9 bolted to the body member over the opening 9 and controlled by a butterfly-type choke valve II. The mixing chamber 8 discharges upwardly into a riser I2, 9 also bolted to the body member 5, communicating with an intake manifold, not shown. The flow of combustible mixture through the riser I2 is controlled by a butterfly throttle valve,knot shown, mounted on a shaft I3 having one end projecting outwardly of the riser. On the projecting end of the shaft I3 is a lever It forming part of the means whereby the position of the throttle valve is controlled.

Within the body member 5 is a large direct passage l5 leading from the inlet opening 9 to the mixing chamber 8 and controlled by a suctionoperated air valve I6. A bypass air passage I1 for primary air leads from the inlet opening 9 around the air valve and terminates in an up- 20 wardly directed venturi I8 discharging into the mixing chamber. The'air valve I6 is of the flap type and is disposed obliquely across the passage I5 with its lower edge pivoted on a horizontal shaft I9 extending transversely of the body member 5 and with its upper and free edge disposed adjacent a side Wall of the member.

The valve, as stated, is operated by suction Within the carburetor which is a function of the degree of throttle opening. Dash pot means is provided for normally maintaining the air valve in position to close the passage I5 and for calibrating the valve to open varying degrees in proportion to the amount of suction within the carburetor. This means comprises a hollow air 35 screw 20 threaded into a stud 20 formed on the body member 5 opposite the inlet opening 9. Slidable within the screw 20 is a piston 2l connected by a rod 22 to the air valve I6 and interposed between the piston 2l and the end of the air screw 20 is a compression spring 23 operating to urge the piston outwardly of the `screw and thereby maintain the air valve I6 yieldably in closed position. By turning the screw 20 into or out of the stud 20', the compression of the spring may be varied thereby varying the extent to which the air valve opens in response to a given suction. A ratchet spring 2li engages serrations on the screw 20 to prevent accidental rotation thereof.

Fuel is supplied to the mixing chamber by a plurality of means supported in the wall portion 'l of the fuel bowl. .At all speeds of the engine, fuel is discharged directly into the mixing chamber 8 through a nozzle 25 vertically disposed and terminating within the venturi I8. At intermediate speeds additional fuel is supplied by a jet 26 mounted on a stand pipe 21 and disposed on the inlet side of the air valve I6 between the upper edge thereof and the adjacent wall of the body member 5. A high speed jet 28 is mounted on a stan-d pipe 29 and is disposed adjacent the lower edge of the air valve I6 but spaced slightly therefrom in the direction of the inlet opening 9. It will be apparent that discharge from the nozzle 25 takes place at all speeds because air is always flowing through the passage I1 when the motor is in operation while the jets 26 and 28 are controlled by the air valve I6 and discharge additional fuel successively as the degree of opening of the air valve increases. The nozzle 25 is threaded into' the Wall portion 1 and the stand pipes 21 and 29 are secured by means of nipples 30 threaded into the wall portion. Y

In order to prevent vapor bubbles from entering the supply passages for the nozzle and jets and cause what is known as vapor lock, the fuel bowl 6 is constructed to provide a float chamber 3I and a sump 32 communicating therewith through a large passage 32 and disposed below the body member 5, the wall portion 1 forming the upper wall of the sump. Extending downwardly into the sump and terminating a short distance from the bottom thereofVV are slender tubes 33 and a stud 34 having a duct 35'formed therein. These tubes and the duct 35 communicate with the nozzle 25 and the stand pipes of the jets 28 and 26 respectively thereby assuring that the fuel will be taken from the bottom of' the sump where, in comparison with the top of the sump, there are few vapor bubbles to enter the fuel supply means. In order further to prevent vapor bubbles from entering the tubes 33 or the duct 35 as the bubbles rise 'from-the bottom of Vthe sump, the tubes are beveled at their lower ends and the stud 34 is formed with a reduced end 34. The tubes and the ductl 35 thus provide extremely small openings through which any bubbles must enter and practically-no flat surfaces below which the bubbles can lodge. The inner surface of the wall portion 1 preferably slopes upwardly toward the passage 32 connecting the sump with the float chamber thereby causing the vapor bubbles to pass upwardly through the passage tol the top of the float charnber where'they will be dissipated.

The supply of fuel to the fuelbowl may be controlled by any conventional means such as a valve generally designated 36 controlled by a float 31. rI'he valve mechanism is hereshown carried by a plate 38 forming the top closure for the fuel bowl. A removable plate 39 constitutes the bottom wall of the sump 32.

Disposed in the duct 35 leading from the sump 32 to the stand pipe of the intermediate speed jet 26 is a calibrated jet 40 discharging into an enlarged portion 35 of the duct. The jet 49 usually is smaller than the jet 26 and in the normal operation of the carburetor governs the amount of fuel supplied by the jet 26, and even when the jet 49 is not smaller it reduces the flow from the jet 26. In order to discharge additional fuel into the carburetor during the power range of operation, auxiliary throttle controlled means is provi-ded for supplying additionalfuel to the intermediate speed jet 26 directly and not through the jet 40. In the present instance, this auxiliary means comprises a duct 4I terminating at one end in the enlarged portion 35' of the duct 35 and communicating at the other end with the float chamber 3 I. At the end communicating with the float chamber 3 I, the duct 4I is controlled by a valve 42 (see Fig. 2) comprising a nipple 43 screwed into a threaded recess 44 and forming at its lower end a valve seat. Cooperating with the valve seat is a valve member 45 having a stem 46 extending upwardly through the nipple and carrying at its upper end a washer 41. The member is urged to valve closing position by means of a compression spring 46 interposed between the washer 41 and a shoulder on the nipple 43. Radial ducts 49 provide communication between the interior of the nipple and the float chamber.

Suitable mechanism is provided for actuating the valve 42 in accordance with the position of the throttle to provide for the supply of additional fuel to the intermediate speed jet during the power range of o-peration. In the present instance this mechanism comprises a cam 59 -disposed above the stem 46 of the valve and fast on a shaft 5! extending transversely of the float chamber 3i with one end projecting outwardly thereof. The outwardly projecting end of the shaft 5I has fixed thereon a crank arm 52 connected by link 53 to a crank arm 54 fixed on the projecting end of the throttle shaft I3. The contour of the cam 56 is such that when the throttle is substantially closed, as shown in Fig. 1, the cam is spaced from the end of the stem 41 permitting the valve member 45 to seat and close the auxiliary fuel supply duct to the intermediate speed jet 26. When the throttle is opened to the extent require-d for the power range of operation, the cam 5l! engages the stem 41 and forces the same downwardly to open the auxiliary supply `duct and permit ow of additional fuel to the intermediate speed jet 26. The point in the extent of throttle opening at which the cam 5l! operates to open the valve 42 may be adjusted to suit the make of engine with which the carburetor is to be employed. It is believed apparent from the foregoing description that the construction results in high fuel economy in that a limited amount of fuel is supplied to the intermediate speed jet as determined by the calibrated nozzle 49 except during the power range of operation when an additional supply is furnished.

Means is provided for automatically varying the degree of throttle opening when the engine is idling in order to prevent stalling of the engine. This means, which is claimed in a division of this application filed May 29, 1935, and bearing Serial No. 23,969, is controlled in accordance with the heat of the engine and in the present instance comprises a cam member 55 rotatable on a stubl shaft 56 secured in the riser I2 and abutted by a set screw 51 of a throttle stop arm 58 fixed on the projecting end of the throttle shaft I3. The periphery of the cam is formed with a dwell surface 55', a stepped portion 55" growing progressively radially away from the axis of the cam and a dwell surface 55". Within an annular housing 55a formed in the cam member 55 is a spirally coiled bimetallic strip 59 having its inner end secured in a sleeve 6D nonrotatably held on the shaft 56 by a nut 6I. The outer end of the bimetallic element 59 engages the cam 55 and rotates the same as the element 59 expands or contracts in accordance with the temperature of the riser. The cam carries a stop pin 62 positioned to abut lugs 63 and 64 on the riser I2 limiting the degree of rotation of the cam. When the engine is cold, the cam will be rotated until the pin 62 abuts the lug 63 in which position the screw 51 of the stop arm 58 rides on the surface 55"' and retains the throttle open a substantial amount to increase the idling speed of the engine and thereby prevent stalling. As the engine warms up, the thermostatic element 59 rotates the cam in counter-clockwise direction as viewed in Fig. l thereby successively decreasing the extent of throttle opening until the engine is thoroughly warmed and idles properly on a minimum throttle opening as determined by engagement of the screw 51 with the surface 55 of the cam.

I claim as my invention:

1. In a carburetor a main body member providing a mixing chamber, and having an air inlet opening anda combustible mixture discharge opening, a fuel bowl providing a float chamber and a fuel sump extending below said. main body member and having a wall portion forming the bottom wall of Said main body member, a direct air passage leading from said inlet opening to the mixing chamber, a suction-operated air valve controlling said passage, a by-pass air passage leading from the inlet opening around said air valve and terminating in a venturi discharging into the mixing chamber, a low speed nozzle mounted on said wall portion to discharge into the venturi and having a'tube extending downwardly through said wall portion into the sump and through the surface of the fuel therein to obtain fuel only from near the bottom of the sump, and an intermediate and a high speed jet controlled by said air valve and mounted on said top wall portion, -said high speed jet having a tube extending downwardly through said wall and through the surface of the fuel in the sump,

and said intermediate speed jet having a passaged extension formed by a stud on the wall portion also extending through the surface of the fuel and downwardly into the sump to a point adjacent the bottom thereof.

2. In a carburetor a main body member providing a mixing chamber, a direct air intake passage leading to the mixing chamber and a by-pass air passage terminating in a venturi discharging into the mixing chamber, a suction-operated air valve controlling the direct passage, a fuel bowl providing a float chamber and a fuel sump extending below said main body member and having an upper wall portion forming the bottom wall of said main body member, a nozzle terminating in the venturi to discharge fuel at all engine speeds, an intermediate speed jet and a high speed jet controlled by said air valve, said nozzle and said jets being threaded into the upper wall of the sump and having portions extending into the fuel sump through theI surface of the fuel therein to a point spaced slightly above the bottom thereof.

3. In a carburetor a main body member providing a mixing chamber and having an open bottom, a fuel bowl providing a float chamber and a fuel sump extending below the main body member and having a wall portion closing the bottom of said main body member, said fuel bowl having a passage providing communication between the fuel sump and the float chamber, and a` plurality of fuel discharge means supported on the wall portion and extending therethrough downwardly into the sump to a point adjacent the bottom thereof, said wall portion having an inner surface inclined upwardly toward the passage between the sump and the float chamber.

4, In a carburetor a main body member providing a mixing chamber and having an air inlet opening and a combustible mixture discharge opening, a direct passage from the inlet opening to the mixing chamber, a suction-operated air valve controlling said passage, a by-pass air passage leading from the inlet opening around said air valve and terminating in a venturi discharging into the mixing chamber, a fuel bowl providing a float chamber and a fuel sump, said fuel sump extending below said main body member and having a top wall portion forming the bottom of said main body member, a low speed nozzle mounted on said wall portion terminating at its discharge end in the venturi and extending downwardly through the wall portion with its intake end disposed adjacent the bottom of the sump, a high speed jet controlled by said air valve also mounted on the top wall portion and extending therethrough to a point adjacent the bottom of thesump, an intermediate speed jet controlled by said air valve and mounted on the top wall portion, a stud extending to a point adjacent the bottom of the sump and having a duct therethrough for supplying fuel to saidintermediate speed jet, a calibrated jet in said duct smaller than said intermediate jet limiting the supp-ly of fuel to the intermediate speed jet under normal operation, an auxiliary fuel supply duct communicating with the normal supply duct for the intermediate speed jet beyond said calibrated jet,

and throttle controlled valve means governing the auxiliary duct to provide additional fuel to said intermediate jet during the power range of operation.

5. In al carburetor a main body member providing a mixing chamber and having an air inlet opening and a combustible mixture discharge opening, a throttle valve controlling the flow of combustible mixture from the chamber, a fuel bowl providing a float chamber and a sump extending below said main body member and having a Wall portion forming the bottom thereof, a direct air passage leading from the inlet opening to the mixing chamber, a suction-'operated air valve controlling said passage, a by-pass air passage leading from the inlet opening around said air valve and terminating in a venturi discharging into the mixing chamber, a low speed nozzle terminating at its discharge end in the venturi and terminating at its intake end adjacent-the bottomv of the fuel sump, a high speed jet controlled by said air valve and mounted on said wall portion, a stud extending downwardly to a point adjacent the bottom of the sump and having therein a normal fuel supply duct for said high speed jet, a calibrated jet in said duct limiting the supply of fuel therethrough, an auxiliary duct for supplying additional fuel to said high speed jet, a valve controlling said auxiliary duct and throttle-actuated cam means operating to open said valve during the power range of operation.

6. In a carburetor a main body member providing a mixing chamber, a throttle controlling the flow of combustible mixture from the chamber, a fuel supply bowl having a sump located below the main body member, a discharge jet including a. stud projecting into the sump to a point adjacent the bottom thereof and having a duct therethrough for providing a normal supply of fuel to said jet, a calibrated jet within said duct limiting the amount of fuel supplied therethrough, an auxiliary duct communicating at one end with the normal supply duct beyond said calibrated jet and communicating at the other end with the fuel supply bowl, a valve controlling said auxiliary duct, and a cam operatively coupled with said throttle operating to open said valve during the power range of throttle opening.

7. In a carburetor a main body member providing a mixing chamber, a throttle controlling the flow of combustible mixture from the chamv ber, a fuel supply bowl, an air Valve controlling in part the supply of air toy the mixing chamber, an air valve controlled jet having a normal fuel supply duct leading from the oat bowl to the jet and including a calibrated jet limiting the fuel supplied to the air valve controlled jet, an auxiliary duct for supplying additional fuel to said air valve controlled jet terminating at one end in said fuel bowl, a valve in the fuel bowl controlling said auxiliary duct, a cam disposed within the fuel bowl in operative relation with respect to said valve, and link means operatively coupling said cam with said throttle, said cam being adapted to open said valve during the power range of throttle opening.

8. In a carburetor a main body member providing a mixing chamber and having an open bottom, a fuel bowl providing a float chamber and a fuel sump extending below the main body member and having a wall portion closing the bottom of said body member, a nozzle mounted on the wall portion and having a slender tube with a bevelled lower end projecting downwardly into the sump, a jet also mounted on said wall portion, and a stud on the wall portion projecting downwardly into the sump, said stud having a duct leading to said jet and terminating in a reduced end portion.

' 9. In a carburetorv ay main body member having an air inlet opening and providing a mixing chamber, a direct passager leading from the inlet opening to the mixing chamber, a suctionoperated air valve controlling said direct passage, a by-pass air passage leading from the inlet opening around said air Valve and terminating in a venturi discharging into the mixing chamber, a fuel bowl providing a float chamber and a fuel sump, a low speed nozzle terminating in said venturi and high speed fuel supply means controlled by said air valve, both said nozzle and said high speed fuel supply means having tubular extensions projecting downwardly into the sump through the upper wall thereof and through the surface of the fuel to a point adjacent the bottom of the sump to draw fuel only from the bottom thereof.

10. In a carburetor a main body member providing a mixing chamber and having an open bottom, a fuel bowl providing a iioat chamber and a sump communicating with the oat chamber and extending below the bottom of said main body member and having a Wall portion forming the top of the sump and closing the bottom of said main body member, and a plurality of fuel nozzles supported onv said wall portion and having passaged extensions projecting downwardly through the upper wall of the sump and through the/upper surface of the fuel therein to a point adjacent the bottom of the sump.

DAVID FIRTH. 

